An electronic circuit is powered using at least two voltage rails, one of which may typically be ground. The voltage rails define a range input signal levels over which the circuit can provide a desired operation. If the voltage of the input signal falls outside of this range, the operation of the circuit may be compromised, and the circuit may even be damaged. Therefore, there is a need to protect the circuit.
In a mobile phone there can be a need to process several analogue single-ended low frequency signals, which can be done by converting the analogue signals to the digital domain for the processing. The analogue signals can be multiplexed, enabling a single analogue-to-digital converter to be used for the conversion of all of the analogue signals. The analogue-to-digital converter can be integrated in a mixed signal integrated circuit operating from voltage rails established by a battery. However, some of the signals to be processed may originate outside of the mixed signal integrated circuit and have a voltage level outside of the operating range of the mixed signal integrated circuit. This circumstance can arise, for example, when the signal to be processed monitors battery charging or a back-up voltage. Such signals can be scaled down to a level within the normal operating range of the mixed signal integrated circuit, but may nevertheless still exceed the battery voltage when the battery is largely discharged. There is a need to provide circuit protection is this circumstance. In addition, there is a need to provide protection when different voltage sources are coupled to different inputs of a multiplexer, to preventing short circuiting between the different voltage sources.
The disclosure relates to improvements in circuit protection.